According to NPR, the heckling came from the Cosecha Movement, a collection of immigrants rights activists who had staged a protest in Detroit earlier that day. In a statement, one of the protestors said,

“I did this because the immigrant community in Michigan is facing a crisis and we need our voices and our demand to be heard: any candidate who claims to be against Trump’s raids and family separations needs to make a real commitment to protect all 11 million undocumented immigrants from detention and deportation. That means using executive authority to stop all deportations on day one in office. We won’t accept empty promises of immigration reform. Obama promised immigration reform and then separated 3 million families. We cannot allow history to repeat itself.”

Later on in the debate, Biden was asked about his involvement with the deportations by Senator Michael Bennet. He didn’t answer the question directly, but rather argued that “to compare [President Obama] to Donald Trump is absolutely bizarre.”

He was pushed again later in the night by Bennet, who asked him to defend his involvement with the high deportation number. He deferred again, only saying, “I was vice president. I am not the president. I keep my recommendation private.”

During the first Democratic presidential debate, Biden took a similar stance. When asked about the deportation number under the Obama administration, he said, “President Obama, I think, did a heck of a job. To compare him to what [Trump] is doing is…close to immoral.”

As many reporters noted online, the number was referencing the amount of deportations that took place under the Obama administration. This isn’t the first time that Biden has faced this number on the campaign trail: earlier this month, families of many of those deported immigrants held a sit-in at Biden’s headquarters in Philadelphia, saying they would refuse to leave until the former vice president apologized.

"3 million deportations" was the chant from a protester in the crowd, referencing the people deported under the Obama administration

As this CNN analysis notes, context is key when discussing deportation numbers and comparing administrations. In fact, the deportation rate has decreased slowly since 2000: more than 12 million people were deported under the Clinton administration, CNN reports, and over 10 million were deported under the Bush administration.

Regardless, the “3 million deportations” chant seemed to strike a nerve with many on Twitter. Erika Andiola, Chief of Advocacy at RAICES, tweeted, “The Obama and Biden administration created the deportation machine that Trump is now using and abusing to deport our communities, detain a record number of people and separate children. We MUST demand an apology from Biden.”

Cory Booker hits Biden hard for ducking de Blasio’s question about whether he backed Obama’s deportations: “You can’t have it both ways. You invoke President Obama more than anyone in this campaign; you can’t do it when it’s convenient and then duck it when it’s not.” #DemDebate